Folic acid as referred to herein includes all substances having folic acid activities and shall not be limited to only pteroylglutamic acid (hereinafter referred to as PteGlu) which is generally said to be folic acid in the narrow sense of the word. In addition to PteGlu, it includes, for example, pteroyl-poly-.gamma.-glutamic acid (hereinafter referred to as PteGlun with n=from 2 to 8), tetrahydrofolic acid, 5-formyl-tetrahydrofolic acid, 10-formyl-tetrahydrofolic acid, 5-methyl-tetrahydrofolic acid, etc.
At present, PteGlu of folic acids is industrially produced through chemical synthesis. Briefly, three components of 2,4,5-triamino-6-hydroxypyrimidine, 1,1,3-trichloroacetone and p-aminobenzoylglutamic acid are condensed in the presence of sodium nitrite in a solution of sodium acetate to give a crude product of folic acid, PteGlu, and the product is purified through recrystallization.
There are some reports disclosing that bacteria of the genera Pseudomonas, Micrococcus, Gluconobacter, Corynebacterium, Aeromonas and Bacillus produce a minor amount (from several tens to one hundred and several tens .mu.g/liter) of a substance having folic acid activities in their cultures (see J. of Bacteriol., 104, 197-201 (1970); Kor. J. Appl. Microbiol. Bioeng., (16), 5, 352 (1988)).
A conventional method for producing folic acid through chemical synthesis is known, in which, however, the raw materials to be used are expensive and the yield of the product is low. Therefore, it is difficult to say that the method is advantageous. As has been mentioned hereinabove, there are some reports disclosing that several species of bacteria produce a substance having folic acid activities in their cultures, but the amount of the substance to be produced is extremely small. Therefore, the proposals disclosed are problematic in that they could not be directly led to the industrial production of the substance.